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Last Updated

09 Jun 2003

Source: New York Times, June 9, 2003

Less Lethal Cousin of Smallpox Arrives in the U.S.


Monkeypox, a viral disease related to smallpox but less infectious and less deadly, has been detected for the first time in the Americas, with at least 23 cases reported in three Midwestern states, the Centers for Disease Control and Prevention said yesterday.

Wisconsin reported 18 cases (15 suspected and 3 confirmed); Illinois reported four (one confirmed); and Indiana reported a single case. The patients ranged in age from 4 to 48 and became ill from May 15 to June 3. All had had direct or close contact with ill prairie dogs, which have become a fad in the exotic-pet market and which might have caught monkeypox from another species, possibly Gambian giant pouched rats; the rats are imported as pets from West or Central Africa, where the disease has long occurred. Monkeypox in Africa is carried mainly by squirrels but named after monkeys because it often kills them.

Several patients in the American outbreak work for veterinarians or pet stores that sold prairie dogs and Gambian rats. No patients have died and four have been hospitalized. Laboratory tests performed at the disease centers in Atlanta yesterday confirmed that the patients had been infected with the monkeypox virus, which belongs to the same orthopox family that includes the virus that causes smallpox.

The monkeypox patients typically fell ill with signs and symptoms like fever, headaches, dry cough, swollen lymph nodes, chills and drenching sweats, Wisconsin health officials said. One to 10 days later, the patients developed rashes consisting of blisterlike pimples that filled with pus, broke open and produced scabs. The rash often erupted in different stages, or crops, as it appeared on the head, trunk and arms and legs. Monkeypox lesions can scar the skin like smallpox or chickenpox.

Most monkeypox patients became ill 4 to 12 days after exposure to a sick animal, but the incubation period may have been as long as 20 days.

The federal disease centers issued a health alert about monkeypox on Saturday night in part out of its concern that doctors who had treated the cases had initially mistaken some for smallpox and chickenpox, said Dr. Stephen M. Ostroff, an epidemiologist at the agency.

Another concern was quickly alerting the public because the cases occurred so recently and because more people could be infected from diseased animals sold in recent days.

By quickly identifying the animals that can be infected with monkeypox, health officials hope to eliminate them before the disease becomes endemic in this country and in the Americas, Dr. Ostroff said. For this and other reasons, the disease centers advised people not to release into the wild live animals suspected of being infected with monkeypox.

Smallpox vaccination can protect against monkeypox, but at least one patient in the current outbreak in this country had been vaccinated for smallpox before routine vaccination was discontinued in 1972.

The disease agency has not recommended a ban on sales of prairie dogs and Gambian rats because the agency is still "in an information-gathering stage," Dr. Ostroff said. But two states, Illinois and Wisconsin, have acted to end their sale and distribution. On Friday afternoon, Wisconsin officials issued a quarantine prohibiting importation, sale and movement of prairie dogs received after April 1 and any nonhuman mammals that come in contact with them. On Saturday night, Gov. Rod R. Blagojevich of Illinois signed an executive order prohibiting sales, import or even public display of these animals.

The federal disease agency is asking physicians, veterinarians and the public to report to their local health departments any rash that develops in people within 21 days of their being exposed to prairie dogs, Gambian rats or other animals.

The agency advised hospital workers caring for suspected monkeypox patients to follow standard infection control measures, including the gloves, gowns and N-95 masks that have been used to protect against SARS. The agency also advised veterinarians to take the same precautions in caring for sick prairie dogs, Gambian rats, other rodents and rabbits.

Monkeypox has long been known to cause sporadic infections in the jungles of West and Central Africa. A sputtering outbreak has been occurring in recent years in Congo.

Up to 10 percent of monkeypox cases have been fatal in West Africa, according to different studies; before smallpox was eradicated, its death rate was about 30 percent.

Studies have shown that outbreaks of monkeypox tend to die out in humans as the virus passes through successive waves, or generations, of cases. This contrasts with smallpox, which continues to spread for centuries until the person-to-person chain of transmission is broken.

The sudden appearance of monkeypox in the United States is a surprise, representing the latest in a series of emerging diseases to reach this country. A prime example is the mosquito-borne West Nile fever, which has spread through the country since it first entered the Americas in 1999.

Precisely how monkeypox reached the United States is unknown. Dr. Ostroff said that the disease agency was investigating possibilities that included the arrival of an infected person or animal from West Africa.

Dr. Kurt Reed, an infectious-disease pathologist who runs the microbiology laboratory and the clinical research center at the Marshfield Clinic in central Wisconsin, said his laboratory had detected the virus in specimens from a 4-year-old girl who had been bitten on the finger by her new pet prairie dog in mid-May.

The girl's parents, who also had contact with the prairie dog, later developed the disease, though the 38-year-old father, who had been vaccinated against smallpox as a child, had a milder case. The monkeypox virus was also detected in a lymph node from the prairie dog, which died a few days later.

The girl went to the clinic with a lesion on her finger, Dr. Reed said, and bacterial cultures quickly ruled out tularemia and the plague. Biopsies of lesions taken from the girl's mother showed a poxlike virus. Cultures from the mother's virus and from the prairie dog matched and suggested an ailment from the orthopox family, Dr. Reed said.

"Right then we knew we had something interesting," he said. "We do lots and lots of virus cultures. This was very unusual. There's nothing really in the literature about prairie dogs having pox viruses."

When the clinic contacted the state health department, the doctors were told of similar cases in the Milwaukee area and learned that the prairie dogs may have been housed with Gambian rats through an exotic pet dealer in suburban Chicago. "That really raised the suspicion that this was an old-world virus that had made its way into the United States," Dr. Reed said.

The disease agency said that the prairie dogs were sold by a Milwaukee animal distributor in May to two pet shops in the Milwaukee area and during a pet "swap meet" in northern Wisconsin. The Milwaukee animal distributor obtained prairie dogs and a Gambian giant rat, which was ill at the time, from a northern Illinois animal distributor. Investigations are under way to trace the source of the animals and to find out where they went, Centers for Disease Control officials said.

Preliminary information suggests that animals from this distributor may have been sold in other states, which the agency did not name.

Prairie dogs and Gambian rats are part of a wide array of exotic animals feeding a growing and diversifying niche pet market, though some animal rights advocates oppose their domestication.

Prairie dogs, plant-eating members of the squirrel family, are believed to have a sophisticated communication system through smell and touch, and they are known to burrow complex tunnel systems.

The rats, which grow to the size of small cats, eat pet food as well as fruits, vegetables and cooked meats.

"They are intelligent, social and can be very gentle if handled from an early age," one enthusiast, Jazmyn Concolor, posted on the Web site www.altpet.net, adding that one rat sleeps with a stuffed toy lion. "They are not pets for everyone, requiring patience and understanding of their habits."

The disease centers urged people to avoid contact with prairie dogs and Gambian rats that have missing patches of fur, rashes or discharges from their eyes or nose, all signs of the illness.

The agency also urged people to wash their hands with soap and water after contact with any animal and to warn doctors and hospitals in advance in seeking medical care if they thought they might be infected.

The disease agency issued no specific treatment recommendations, but scientists are testing an antiviral drug, cidofovir, for its efficacy.